Background

Apparently there are two traces that have been interrupted which would allow serial port access.

These traces have been interrupted UNDER a SMD capacitor at position C54. Junker[1] (see Yamasita's article/reference) discovered
the way first[2]. Apparantly the pinheaders from the SCON-KIT/ PRO can be fit into the case quite easily as well[3].

Method

Then you will need to find some way to resurrect the traces that are interrupted under C54.

C54

We need to fix these wires which go under C54:

Method 1: reconstruct the traces (on the backside)

This method requires absolutely no soldering.

Lay a layer of a scotch tape between holes, just not to cover them.

Use a strand of high flexible low oxygen copper wire.

Thread it through both holes.

Fix it with a scotch tape on the back side.

Cut remainders on the front side, leaving about 2 mm.

Repeat from step 2 with the second thread.

Be sure not to shorten anything else.

Holes marked in RED

Use a strand of high flexible low oxygen copper wire, thread it through both holes and fix it with a scotch tape on the back side

Cut remainders on the front side, leaving about 2 mm

Method 2: Bridge the traces (on the frontside)

This method requires a steady hand and good soldering skills.

Use two strands of high flexible low oxygen copper wire.

Locate and carefully remove C54 from its pads.

Clean the area with rubbing alcohol and a tiny brush.

Cut two stands of high flexible copper wire to length.

Solder each of the strands to the vertically aligned pads.

Resolder C54 to its' original position.

Ensure no shorting has take place while soldering.

Locate C54 on the upper (processor) side of the PCB.

Carefully remove C54 (we need it later) from it's pads.

Using two strands of high flexible copper wire, solder each of the two vertically aligned traces.

Pinout of Port

Wire colors referenced in table

Pin

Signal

Wire Color

1

Transmit (TxD)

Green

2

Receive (RxD)

White

3

Power 3.3V (Vcc)

NC

4

Ground (GND)

Red

Use a Level Shifter

The serial port signals from the processor are only 3.3V. For proper RS-232 12V signaling, an RS-232 level shifter needs to be added. These are very common in PDA serial cables also, but can be purchased

Models other than KuroPro

If you are attaching a serial header pin onto the main board, you may want to consider:

Using the header pin unit with a 90 degree bend, or you might not be able to close the case

Soldering it with the pins toward the interior, rather than toward the case. This allows easier access, since if the pins face the case side they would be very close to the metal side. This would make access is so tight that one might end up taking the board out to get plug fitted on the pins.

Solder the 4-pin header to the board. Make sure you don't have shorts.

You will need to switch wires on the TTL-232R-3V3 cable. Use a sharp object to lift the plastic tabs and carefully pull the wires out. Rearrange them according to the table above (black, empty, orange, yellow, empty, empty) and slide those wires back in. Tape the other wires to make sure they don't short anything.

When plugging in the cable, make sure black aligns with GND, yellow with TXD, and orange with RXD.

Connect the USB cable to your computer, start a terminal program with the right settings.

Turn on the device, you should see output from the bootloader in couple seconds.